The ability to introduce manipulated genes and delete or modify endogenous genes in the germline of animals is a major technological advance in biology, enabling investigators to answer questions about gene function which must be analyzed in a whole animal model system. Transgenic and knockout animals have been instrumental in providing insights into mechanisms of developmental gene regulation, cellular interactions within the immune system, and the effect of oncogenes on growth and differentiation. Demand for these services has remained high during the current review period. In 2009, 67 requests were completed, and ninety-four percent (94%) of Facility usage was by peer-reviewed, funded investigators for this service. In addition, the Facility's cryopreservation service is highly utilized, resulting in freezing of 106 lines during the period 2005-2009, providing important insurance against the loss of irreplaceable mouse lines in the event of a catastrophic event in the Transgenic Mouse Facility (TMF). Over the past five years all five of the CCSG Programs have used the Facility. The Facility has recently added and validated the capacity to carry out Zinc finger nuclease (ZFN)-mediated gene targeting, a methodology that considerably accelerates and simplifies the generation of knockout and knock-in mice, and allows generation of complex mouse models with multiple genetic alterations that were not previously feasible. Kappes (Immune Cell Development and Host Defense (ICDHD) Program), has directed this resource since 1995 and has responsibility for Facility operations. Equitable access to the Facility is assured by Facility policy, oversight from a user facility advisory committee and a governing Facilities Parent Oversight Committee (FPOC).